We all know about the carbon in Earth’s atmosphere, and probably about the carbon contained in plants and the bodies of animals. But a substantial fraction of the carbon in the planet’s land-based ecosystems is held in something so obvious we might overlook it: soil.
We analysed more than 200,000 soil measurements from around the world to calculate that the top two metres of soil globally holds about 2.3 trillion tonnes of inorganic carbon. This is about five times more carbon than found in all the world’s terrestrial vegetation. We estimate some 23 billion tonnes of this carbon may be released over the next 30 years, with poorly understood effects on Earth’s lands, waters and atmosphere.
Soil carbonates can come either from weathering of rocks or from the reaction of soil minerals with atmospheric carbon dioxide. In wetter regions, soil carbonates may also be found along rivers and around lakes and coastal areas, in the form of calcium-rich alluvial deposits or calcareous rocks. Soils in karst regions – areas rich in rocks like limestone, and often characterised by caves and sinkholes – typically contain carbonate in rocks. In areas such as central Asia large deposits of wind-blown sediments contribute to the accumulation of carbonate minerals.
Scientists have viewed carbonates in soil as a relatively stable pool of carbon that changes only slowly over time. However, human activities have made soil inorganic carbon more mobile. Irrigation and fertilisation of farmland speed up the rate at which soil inorganic carbon is dissolved and leaches out of the soil.
In our research, we found that 1.13 billion tonnes of inorganic carbon are lost from soils each year to inland waters. This loss has profound yet often overlooked effects on carbon transport between the land, freshwater bodies, the atmosphere and the oceans.
Carbon Cycle Carbon Sequestration Climate Change Enhanced Weathering Environment Environmental Science Precision Agriculture Soil Carbon Soil Science
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